From: Phrogz <phrogz@...>
Date: 2007-11-22T06:50:07+09:00
Subject: Re: AR: many to many with attributes

On Nov 21, 7:12 am, Christian Kerth <christian.ke...@dynamicmedia.at>
wrote:
> > 1) Do your models look like this:
> >http://matthewman.net/2006/01/06/rails-activerecord-goes-through/
>
> @1) yeah, i have set up the models with :through associations. The all
> work.

My question, which I didn't explain well, was: did you create a Model
for the many-to-many table?


> > 2) This is a rails question, not a Ruby one. Try the rails list.
>
> @2) Why is this a Rails question? I'm using ActiveRecord without
> Rails...

Ah, OK then. As I suspect you know, most people using AR are using
Rails. My apologies for the assumption. Nonetheless, given that fact,
that list seems most likely to have people able to answer your
question.

...if this doesn't answer it:

C:\tmp\db>sqlite3 development.sqlite3
SQLite version 3.5.2
Enter ".help" for instructions
sqlite> .dump
BEGIN TRANSACTION;
CREATE TABLE schema_info (version integer);
INSERT INTO "schema_info" VALUES(3);
CREATE TABLE books ("id" INTEGER PRIMARY KEY NOT NULL, "author"
varchar(255) DEFAULT NULL);
CREATE TABLE languages ("id" INTEGER PRIMARY KEY NOT NULL, "langcode"
varchar(255) DEFAULT NULL);
CREATE TABLE book_publishings ("book_id" integer DEFAULT NULL,
"language_id" integer DEFAULT NULL, "title" varchar(255) DEFAULT
NULL);
COMMIT;


C:\tmp\app\models>type *.rb

book.rb
class Book < ActiveRecord::Base
  has_many :book_publishings
  has_many :languages, :through=>:book_publishings
end

book_publishing.rb
class BookPublishing < ActiveRecord::Base
  belongs_to :book
  belongs_to :language
end

language.rb
class Language < ActiveRecord::Base
  has_many :book_publishings
  has_many :books, :through=>:book_publishings
end


c:\tmp> ruby script\console
Loading development environment.

>> cat_book = Book.create :author=>'me'
=> #<Book:0x474355c @errors=#<ActiveRecord::Errors:0x46bcb9c
@errors={}, @base=#<Book:0x474355c ...>>,
@new_record_before_save=true, @attributes={"author"=>"me", "id"=>1},
@new_record=false>

>> english = Language.create :langcode=>'en'
=> #<Language:0x46a6900 @errors=#<ActiveRecord::Errors:0x46a41c8
@errors={}, @base=#<Language:0x46a6900 ...>>,
@new_record_before_save=true, @attributes={"id"=>1, "langcode"=>"en"},
@new_record=false>

>> german = Language.create :langcode=>'de'
=> #<Language:0x469fe84 @errors=#<ActiveRecord::Errors:0x469f754
@errors={}, @base=#<Language:0x469fe84 ...>>,
@new_record_before_save=true, @attributes={"id"=>2, "langcode"=>"de"},
@new_record=false>

>> BookPublishing.create :book=>cat_book, :language=>english, :title=>'My Cat is Awesome'

=> #<BookPublishing:0x4688608 @book=#<Book:0x474355c
@errors=#<ActiveRecord::Errors:0x46bcb9c @errors={}, @base=#<Book:
0x474355c ...
>>, @new_record_before_save=true, @attributes={"author"=>"me", "id"=>1}, @new_record=false>, @errors=#<ActiveRecord::Errors:0x4684ec
c @errors={}, @base=#<BookPublishing:0x4688608 ...>>,
@language=#<Language:0x46a6900 @errors=#<ActiveRecord::Errors:
0x46a41c8 @error
s={}, @base=#<Language:0x46a6900 ...>>, @new_record_before_save=true,
@attributes={"id"=>1, "langcode"=>"en"}, @new_record=false>, @
attributes={"title"=>"My Cat is Awesome", "id"=>1, "language_id"=>1,
"book_id"=>1}, @new_record=false>

>> BookPublishing.create :book=>cat_book, :language=>german, :title=>'Meine Katze ist genial'
=> #<BookPublishing:0x467e158 @book=#<Book:0x474355c
@errors=#<ActiveRecord::Errors:0x46bcb9c @errors={}, @base=#<Book:
0x474355c ...>>, @new_record_before_save=true,
@attributes={"author"=>"me", "id"=>1}, @new_record=false>,
@errors=#<ActiveRecord::Errors:0x467d5c8 @errors={},
@base=#<BookPublishing:0x467e158 ...>>, @language=#<Language:0x469fe84
@errors=#<ActiveRecord::Errors:0x469f754 @errors={}, @base=#<Language:
0x469fe84 ...>>, @new_record_before_save=true, @attributes={"id"=>2,
"langcode"=>"de"}, @new_record=false>, @attributes={"title"=>"Meine
Katze ist genial", "id"=>2, "language_id"=>2, "book_id"=>1},
@new_record=false>

>> cat_book.languages.map &:langcode
=> ["en", "de"]

>> cat_book.book_publishings.map &:title
=> ["My Cat is Awesome", "Meine Katze ist genial"]

>> cat_book.book_publishings.find_by_language_id( english.id )
=> #<BookPublishing:0x4668038 @attributes={"title"=>"My Cat is
Awesome", "language_id"=>"1", "book_id"=>"1"}>


Note that due to the crazy magic of AR, that last line is a single SQL
query:
SELECT * FROM book_publishings
WHERE (book_publishings.book_id = 1) AND
(book_publishings."language_id" = 1)
LIMIT 1